You can examine detailed documents about Virtual Private Database which is an important topic in Oracle database.
First of all, you should start from article 1 to understand what is Virtual Private Database and understand its general architecture logic.
Next, you should read the second article to understand examples and various rules.
Finally, I recommend that you look at our latest article to see policy definitions and examples of application context.
See you in next series.
Do you want to learn Oracle Database for Beginners, then read the following articles.
https://ittutorial.org/oracle-database-19c-tutorials-for-beginners/